Thermochimica Acta 411 (2004) 171–176 Estimation of interfacial behavior using the global phase diagram approach I. Carbon dioxide–n-alkanes Andres Mej´ ıa a , Ilya Polishuk b,∗,1 , Hugo Segura a , Jaime Wisniak b a Department of Chemical Engineering, Universidad de Concepción, Concepción, Chile b Department of Chemical Engineering, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel Received 11 June 2003; received in revised form 11 August 2003; accepted 18 August 2003 Abstract This study looks for the first time at the possibility of predicting the interfacial tension in mixtures without preliminary resource to their experimental data. For this purpose the quantitative global phase diagram (klGPD)-based approach (GPDA), which needs only two or three key experimental points of one homologue for predicting the complete phase behavior in whole homologues series of binary systems, is combined with the gradient theory (GT) methodology. The resulting model is able to predict the data in satisfactory manner, although the increasing asymmetry between the compounds of the mixture probably affects the ability of GPDA to yield accurate predictions of phase equilibria and interface tension simultaneously. © 2003 Elsevier B.V. All rights reserved. Keywords: Surface tension; Predictive model; Equation of state; Parameter optimization; Carbon dioxide; n-Alkanes 1. Introduction A vast body of literature has been devoted to the develop- ment of thermodynamic models for the prediction and cor- relation of vapor–liquid equilibria (VLE), but modeling of other very important thermodynamic properties such as in- terfacial tension, has not received so far significant attention. Data on interfacial tension are necessary for the description of phenomena that take place at interfacial boundary layers and which define the efficiency of industrial processes such as mass transfer during extraction, heat transfer under boil- ing conditions, flow in porous catalytic media, enhanced oil recovery, etc. For example, the interfacial tension data of carbon dioxide–hydrocarbon mixtures suggest that CO 2 can be very effective as an oil-displacing agent. Sahimi and Taylor [1] have demonstrated that the method based on the gradient theory (GT), first developed by van ∗ Corresponding author. Tel.: +972-86477930; fax: +972-86472916. E-mail addresses: amejia@diq.udec.cl (A. Mej´ ıa), polishyk@bgumail.bgu.ac.il (I. Polishuk). 1 Present address: The Department of Chemical Engineering and Biotechnology, The College of Judea and Samaria, Ariel, Israel. der Waals and lately reformulated by Cahn and Hilliard [2], is more efficient and accurate than the principle of two-scale factor universality (TSFU). Hence, the GT-based approach seems today to be the most promising way to model the interfacial tension in mixtures. The GT approach is based on the mean field approximation that describes a continu- ous evolution of the density of the Helmholtz energy along the interface and thus it allows description of the interfa- cial properties such as concentration profile and interfacial tension in mixtures. The GT-based approach requires the values of the density of the Helmholtz energy of the homogeneous mixture and the influence parameters of the non-homogeneous mixture. The density of the Helmholtz energy can be estimated using an equation of state (EOS) of the homogeneous mixture while the influence parameters, which carry the information on the molecular structure of the interface, are obtained by fitting the interfacial tension data of pure compounds. It should be noticed that the principal advantage of this approach is the fact that common EOS models can be used to calculate the interfacial behavior and the phase equilibrium condition. Carey [3], Cornelisse [4], Kahl and Enders [5,6] and Poster and Sanchez [7], have discussed in depth the modeling 0040-6031/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2003.08.006